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How Personal Air Vehicles Work


Inside the Springtail
Springtail EFV-4A during a free hover in October 2003
Springtail EFV-4A during a free hover in October 2003
Photo courtesy trekaerospace.com

Four major components of the Springtail might someday enable it to fly us to work or the local movie theater:

  • 118-horsepower rotary engine
  • Drivetrain that drives the ducted fan blades
  • Counter-rotating ducted fans (two)
  • Fly-by-wire control system

At the heart of this patented vehicle is a small 118-horsepower rotary engine that uses 100-octane aviation gasoline (AVGAS). If necessary, it will run on 91-octane and there's a Springtail engine that actually uses diesel. A rotary engine is an internal combustion engine, like the engine in your car, but it works in a completely different way than the conventional piston engine.

Like a piston engine, the rotary engine uses the pressure created when a combination of air and fuel is burned. In a piston engine, that pressure is contained in the cylinders and forces pistons to move back and forth. The connecting rods and crankshaft convert the reciprocating motion of the pistons into rotational motion that can be used to power a vehicle.

The pressure of combustion is contained in a chamber formed by part of the housing and sealed in by one face of the triangular rotor, which is what the engine uses instead of pistons. The rotor follows a path that looks like something you'd create with a Spirograph. This path keeps each of the three peaks of the rotor in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it and makes useful power as the gases expand, and then expel the exhaust.

Springtail EFV specifications sheet
Springtail EFV specifications sheet
Photo courtesy trekaerospace.com

The Springtail's engine is connected to a system of drive shafts, universal joints and gear boxes, which drive the counter-rotating ducted fans. Earlier models sported fixed-pitch fan blades (as opposed to variable-pitch), meaning they are rigidly fixed to the central rotating fan hub at a set angle. Fixed-pitch blades helped to reduce the number of moving parts at work on the earlier models. However, the downside of fixed-pitch blades is that they cannot be adjusted during flight. Being the latest model, the Springtail EFV-4B now features several technological upgrades and improvements -- including variable-pitch blades. Another major improvement is the Springtail's new control system.

Let's take a closer look at that new system.